libbpf-rs: Implement Send for PerfBuffer and RingBuffer

As per
#224 (comment)
ring buffers and perf buffers can be polled from any thread. Hence, it
is safe for us to implement `Send` for the corresponding Rust types,
`RingBuffer` and `PerfBuffer`.

Closes: #224
Signed-off-by: Daniel Müller <deso@posteo.net>

Author: d-e-s-o

libbpf-rs/src/perf_buffer.rs

@@ -220,10 +220,30 @@ impl<'b> PerfBuffer<'b> {
     }
 }
 
-impl<'b> Drop for PerfBuffer<'b> {
+// SAFETY: `perf_buffer` objects can safely be polled from any thread.
+unsafe impl Send for PerfBuffer<'_> {}
+
+impl Drop for PerfBuffer<'_> {
     fn drop(&mut self) {
         unsafe {
             libbpf_sys::perf_buffer__free(self.ptr);
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    /// Check that `PerfBuffer` is `Send`.
+    #[test]
+    fn perfbuffer_is_send() {
+        fn test<T>()
+        where
+            T: Send,
+        {
+        }
+
+        test::<PerfBuffer>();
+    }
+}

libbpf-rs/src/ringbuf.rs

@@ -178,7 +178,10 @@ impl<'a> RingBuffer<'a> {
     }
 }
 
-impl<'a> Drop for RingBuffer<'a> {
+// SAFETY: `ring_buffer` objects can safely be polled from any thread.
+unsafe impl Send for RingBuffer<'_> {}
+
+impl Drop for RingBuffer<'_> {
     fn drop(&mut self) {
         unsafe {
             if !self.ptr.is_null() {
@@ -187,3 +190,20 @@ impl<'a> Drop for RingBuffer<'a> {
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    /// Check that `RingBuffer` is `Send`.
+    #[test]
+    fn perfbuffer_is_send() {
+        fn test<T>()
+        where
+            T: Send,
+        {
+        }
+
+        test::<RingBuffer>();
+    }
+}